my trusty Asus EN6600GT board recently died, so I was forced to buy a new one, and chose an EN7600GT due to it's two DVI ports.
Since then, stability problems struck me - the system often completely locks up to the point where even SysReq+s / u won't work any more.
None of the problems I encountered where present with the old gfx board, and I didn't change the system configuration in between.

the system often locks up when starting a new game in UT2004, but it also randomly happened in NWN and on several other occasions.
A less severe crash happened several times when scrolling in kolourpaint: the screen freezes, the mouse can still be moved, but no gui is responding. ssh-login is still possible, dmesg saying:
NVRM: Xid (0001:00): 6, PE0000 0404 ffffffff 0000fdec ffefefef 00086400

I've tried reinstalling the drivers and using different driver versions:

nvidia-drivers-1.0.8776 -> locks up
nvidia-drivers-1.0.9629 -> locks up
nvidia-drivers-1.0.9742 -> no deadlocks during my first round of UT, but several other applications stopped working properly, so it's not an option and I didn't test further.